This invention is related to abrasive dental tools and instruments, more particularly to dental tools such as dental burs, scrapers and similar scraping tools, which have polycrystalline diamond layers as abrasive surfaces.
Abrasive dental tools and surgical instruments used in medically treating teeth of human beings, and in some instances animal teeth, carry abrasive particles on the tool surfaces applied for grinding teeth and bones in such treatments. The abrasive materials, most frequently polycrystalline diamond particles, are carried on a shank, which is supported securely in some type of a hand held drill or similar equipment, when in use. The shank is most commonly made of stainless steel or a similar tough, corrosion resistant, hard metal such as tungsten, or hard metal alloys. The shank is usually, but not necessarily, an elongated cylindrical body or rod. The abrasive layer of polycrystalline diamonds is usually applied as an adherent layer to an end portion of the shank only. The grinding action exerted by the abrasive particles is often enhanced by rotation of the shank at high speed.
The abrasive polycrystalline layer of polycrystalline diamond particles can be formed or deposited on the metallic shank in known ways, such as polycrystalline diamonds embedded in a nickel or nickel alloy matrix, or alternatively, embedded in a coating of polyurethane or similar hard polymer applied as a base coating onto the appropriate portion of the shank. The latter method of utilizing a polymer as a binding matrix for already formed diamond particles is described in U.S. Pat. No. 5,273,559, issued to Hammar et al. on Dec. 28, 1993. A dental bur shaped as a wedge bearing a thin cutting edge and having titanium or tungsten nitride or carbide formed by vapor deposition over the cutting edge is described in U.S. Pat. No. 4,681,541 which issued to A. A. Snaper on Jul. 21, 1987. Another method of obtaining an abrasive polycrystalline diamond layer is by chemical vapor deposition (CVD) from an ionized carbon bearing plasma. A polycrystalline diamond layer deposited directly over an end portion of the metal shank by high temperature vapor deposition is one of the preferred ways of obtaining polycrystalline diamond layers. However, one of the disadvantages of vapor deposited polycrystalline diamond layers is brittleness and low impact resistance.
Sterility and appropriate anti-bacterial conditions play a very important role in any intervention in the human or animate body, hence it is imperative that the abrasive surface bearing dental tool should be subjected to sterilization in the usual manner, before use. Hence the dental tool bearing the abrasive surface must be able to withstand the conditions of chemical and/or steam sterilization.
Another problem area which may arise with utilizing dental tools bearing polycrystalline diamond layers, is that the deposited layers occasionally have small crevices and similar discontinuities, which may subsequently give rise to dislodging and loss of small diamond crystals when in use as an abrasive tool or dental bur.
It is desirable to have a protective or encapsulating coating over the abrasive surfaces of polycrystalline diamonds, which can provide protection during packaging, transport, general handling and sterilization. It is noted that the present invention is directed to protection of the abrasive surface and bears little relation to how the abrasive surface has been obtained.
The object of the present invention is to provide a protective coating over the abrasive surface comprising polycrystalline diamonds during packaging, storing and sterilization, which coating is automatically removed from the cutting surfaces of the polycrystalline diamond layer when brought into contact with the teeth, bone, porcelain or other dental ceramic materials during a dental preparation or dental treatment procedure.
In one embodiment of the invention a tough polymer coating, which is capable of withstanding the conditions of sterilization, is applied to encapsulate the polycrystalline diamond layer directly after manufacturing, or after depositing the diamond layer over the appropriate surface of the shank or substrate. The protective capabilities of the polymer coating can be further increased by admixing hard ceramic materials of very small particles size in amounts up to 40 wt. % based on the weight of the polymer in the coating.
In another embodiment of the invention a malleable metallic layer, such as nickel, copper or an alloy of nickel or/and copper, or an alloy of copper-tin-titanium, which is softer than diamonds, is deposited by known means over the layer of polycrystalline diamond directly after manufacturing and/or subsequent to depositing the diamond layer over the appropriate surface of the shank or substrate.